The pallet clamping device arranges the workpiece at a leading-end operating position of the machine head via the gripped pallet, and the pallet for changing is arranged at the set-up station.
In conventional techniques, in the case of changing a pallet with the pallet clamping device, an external device is used to convey the pallet between the clamping device and the set-up station.
Further, conveyance of the pallet is with no relation whether the pallet clamping device is a movable type or a fixed type.
In typical system, the pallet is conveyed by a pallet changing arm device capable of expanding and reducing an arm in a multiple stage or a pallet changing arm device capable of moving in itself.
However, since the pallet changing arm device capable of expanding and reducing the arm needs a larger installation space and the device only changes a pallet one by one, it inevitably needs a longer time to change a pallet.
On the other hand, the movable-type pallet changing arm device inevitably needs a control device for moving and stopping the arm, and the control device inevitably requires a more complicated configuration than the pallet changing arm device capable of expanding and reducing the arm.
In Patent Document 1 in which the patent right was obtained by applicant, attention is taken to the fact that a spindle which moves at the leading-end portion of the machine head is able to move freely, and so a pallet for machining is gripped by a spindle head on one side of a pallet changing arm (a pallet gripping arm), whereas a pallet for changing is gripped on the other side thereof. Thereby, when the spindle head descends, the pallet changing arm is allowed to ascend and, thereafter, the pallet changing arm is rotated, by which the pallets are changed efficiently.
In the above-described configuration, the pallet changing arm also acts as the pallet clamping device, and so, an ascending mechanism necessary for changing a pallet is relatively simple.
However, the above-described pallet changing arm needs an external driving device for moving the pallet changing arm and is placed over an operating position of the spindle head and the set-up station. So, above-described configuration inevitably needs a long and large space resultingly.
In Patent Document 2, a shoulder rail is provided on a pallet changing arm which can turn, and a pallet for changing is allowed to move on the rail. In above-described configuration, a mechanism of expanding and reducing the pallet changing arm or a mechanism of moving the pallet changing arm is unnecessary, and so may improve the conventional techniques.
However, the above-described configuration inevitably needs such another special control that in the case of pallet for changing being moved from an end portion side of the pallet changing arm to the center side of turning, the other pallet for supporting a workpiece which has been already machined by another operation is ascended and, contrary in the case of the other pallet being moved from the center position of the turning of the pallet changing arm to the end portion side thereof, the pallet for changing is descended.
In Patent Document 3, the leading end sides of intermediate portions on both sides of the pallet changing arm are supported pivotally at an upper perpendicular region so as to rotate freely and the leading end sides may be kept in upper position along perpendicular direction, with a certain angle according to the horizontal direction. Thereby, the pallet clamping device is compact in space and a pallet gripped by the pallet clamping device is changed by a simple configuration to improve the conventional techniques.
However, in the configuration disclosed in the above-described Patent Document 3, it is inevitably necessary to control the rotation of the arm on one side which takes out the pallet gripped by the pallet clamping device. And, such a mechanism invites another complex procedure which is different from in the conventional techniques.
Considering above-described conventional techniques and publicly known techniques such as Patent Documents 1, 2, and 3, it is apparent that pallet changing system which utilizes the moving function itself of the machine head for conveying a pallet has not been proposed, though the machine head of operating the spindle is capable of movement.